The present invention relates to a bucket wheel sluice gate and in particular to a gate for dispensing predetermined amount of granular materials from a bulk source to given user.
In general, a bucket wheel gate comprises a cylindrical housing, having a feed inlet opening to a source, such as a silo of granulate material and a discharge outlet opening to a processing user of the material. Located within the housing is a wheel formed of a plurality of radially disposed blades forming, between adjacent blades, cells or bucket chambers, which as the wheel rotates are filled with the granulated material entering the feed inlet and are discharged as the feed cavity passes the discharge opening.
Efforts have been made to prevent overfilling of the individual cells of the bucket wheel both when the bucket wheel is at a standstill, and when the wheel is being rotated. Such overfilling causes the excess bulk material to be squeezed between the edges of the blade and the edges of the housing defining the cross-section of the feed inlet and discharge outlet in the direction of rotation of the wheel. This is a particular problem in that should the bulk material become lodged between these edges, the bucket wheel may be difficult or impossible to start from a standstill position. Even during operation, the shearing off of the bulk material at the aforementioned edges leads to considerable development of noise, an increased demand for driving power and greatly increases wear on the wheel components as well as the motive means. In addition, the granular structure of the bulk material is itself destroyed.
In order to avoid overfilling of the cells of the bucket wheel, when in the standstill condition, a shut-off device such as a shutter or valve is generally provided in the inlet. Two other possibilities for avoiding overfilling during operation have also been simultaneously attempted. One method provides for an arrangement in which the inlet or the inlet cross section is layed out eccentrically in relation to the central axis of the housing which axis passes through the shaft of the bucket wheel. In this manner, with a suitable division of the bucket wheel into individual cells or chambers, the natural angle or slope (a/k/a angle of repose; German=natuerliche Boeschungswinkel) of the bulk material insures that the chambers in communication with the inlet are only partially filled. As used in the foregoing text, the term "Boeschungswinkel" means the angle between the horizontal plane and the natural slope of the mass of bulk material, deposited on this horizontal plane for example by emptying a bag. The angle of this natural slope is a characteristic feature of the specific bulk material and is related mainly with the internal coefficient of friction the material. Another possibility made use of in the known bucket wheels provides for a reduction in the cross section, of the feed inlet, by employing an baffle in the inlet. This baffle insures that at any rate of operation, starting from the rated rotational speed of the bucket wheel, the quantity of bulk material fed to each chamber is smaller than the volume of the cell or chamber traversing the inlet. This arrangement is similar to that earlier described in that the cells or chambers are only partially filled.
In any case, the prior art attempts, noted above, have a decided disadvantage in that the dosing volume of the gate cannot be utilized completely since there is no assurance that there is uniformity even in the partial filling of each cell and that a control of the dosing by changing the speed of the bucket wheel can only be made within a very limited range.
In another attempt, the baffle was provided with a prestripping edge by which the overfill was moved aside before filling the chambers. Despite the use of such a prestripping edge, the grains of bulk material inevitably accumulate on the edge surfaces of the blades as well as in the area lying in front of the housing edge in the running direction so that they become jammed and sheared off between the front edge of the blade and the edge of the housing. This necessitates not only an increased demand for driving power but causes a characteristic hacking noise as well as increased wear in the gate. In addition, the baffle of this type is only effective when the gate is at operative speed since the chambers are overfilled even at a standstill. In this condition, starting difficulties, or even a blockage of the drive motor may occur when the wheel is again turned on.
In order to at least reduce the additional requirement for drive power and avoid the development of noise it is known to form the first edge of the housing traversed by the blade in the running direction after passing the inlet, so that it extends not in parallel to edge of the blades but at an angle to the blades so that the grains of the bulk material are no longer sheared off simultaneously but sequentially. In any event, this attempt did not eliminate shearing or jamming nor the need for increased power nor the elimination of noise.
The present invention has as its object the production of a bucket wheel gate in which the shearing off of grains of bulk material between the engaging edges of the blades and the housing are avoided in every state of operation.
It is another object of the present invention to provide a bucket wheel gate by which increased speed and more accurate dosing can be obtained.
The foregoing objects together with other objects and advantages will be apparent from the following description.